|
In gynecology, the Papanikolaou test (also called Pap smear, Pap test, cervical smear, or smear test) is a medical screening method for detecting infectious, premalignant, and malignant processes in the ectocervix, endocervix and endometrium. The pre-cancerous changes (called dysplasias or cervical or endocervical intraepithelial neoplasia) are usually caused by sexually-transmitted human papillomaviruses (HPVs). The test aims to detect and prevent the progression of HPV-induced cervical cancer and other abnormalities in the female genital tract by sampling cells from the outer opening of the cervix (latin for "neck") of the uterus and the endocervix. The sampling technique changed very little since its invention by Georgios Papanikolaou (1883–1962) to detect cyclic hormonal changes in vaginal cells in the early 20th century until the development of liquid based cell monolayer technology. The test remains a highly effective, widely used method for early detection of cervical cancer and pre-cancer. It is generally recommended that sexually active females seek Pap smear testing annually, although guidelines may vary from country to country. If results are abnormal, and depending on the nature of the abnormality, the test may need to be repeated in three to twelve months. If the abnormality requires closer scrutiny, the patient may be referred for detailed inspection of the cervix by colposcopy. The patient may also be referred for HPV DNA testing, which can serve as an adjunct (or even as an alternative) to Pap testing. About 5% to 7% of pap smears produce abnormal results, such as dysplasia, possibly indicating a pre-cancerous condition. Although many low grade cervical dysplasias spontaneously regress without ever leading to cervical cancer, dysplasia can serve as an indication that increased vigilance is needed. Endocervical and endometrial abnormalities can also be detected, as can a number of infectious processes, including yeast and trichomonas. A small proportion of abnormalities are reported as of "uncertain significance".
Technical aspects Samples are collected from the outer opening or os of the cervix using an Aylesbury spatula or (more frequently with the advent of liquid-based cytology) a plastic-fronded broom. The cells are placed on a glass slide and checked for abnormalities in the laboratory. Since the mid-1990s, techniques based around placing the sample into a vial containing a liquid medium which preserves the cells have been increasingly used. The media are primarily ethanol based. Two of the types are Sure-Path (TriPath Imaging) and Thin-Prep (Cytyc Corp). Once placed into the vial, the sample is processed at the laboratory into a cell monolayer, stained, and examined by light microscopy. The liquid sample is also suitable for low and high risk HPV testing. Proper sample acquisition is crucial to the accuracy of the test; clearly, a cell that is not in the sample cannot be evaluated. Even liquid based pap smears have a false negative rate of 15-35% and for that reason ACOG and ASCCP have recommended the use of HPV testing in addition to the pap smear in all women over the age of 30. By adding the more sensitive HPV test, which identifies the HPV virus itself, the sensitivity of the pap smear is improved to nearly 100%. In the last decade there have been successful attempts to develop automated, computer image analysis systems for screening. One of these has been FDA approved and functions in high volume reference laboratories, with human oversight. The sample is stained using the Papanicolaou technique, in which tinctorial dyes and acids are selectively retained by cells. Unstained cells can not be visualized with light microscopy. The stains chosen by Papanicolau were selected to highlight cytoplasmic keratinization, which actually has almost nothing to do with the nuclear features used to make diagnoses now. The sample is then screened by a specially trained and qualified cytotechnologist using a light microscope. The terminology for who screens the sample varies according the country; in the UK, the personnel are known as Cytoscreeners, Biomedical scientists (BMS), Advanced Practitioners and Pathologists. The latter two take responsibility for reporting the abnormal sample which may require further investigation. In the United States, physicians who fail to diagnose cervical cancer from a pap smear have been convicted of negligent homicide. In 1988 and 1989, Karen Smith had received pap smears which were argued to have "unequivocally" shown that she had cancer; yet the lab had not made the diagnosis. She died on March 8 1995. Later, a physician and a laboratory technician were convicted of negligent homicide. These events have led to even more rigorous quality assurance programs, and to emphasizing that this is a screening, not a diagnostic, test, associated with a small irreducible error rate. Practical aspects The physician or operator collecting a sample for the test inserts a speculum into the patient's vagina, to obtain a cell sample from the cervix. A pap smear appointment is normally not scheduled during menstruation, and patients should avoid contamination of the vagina and uterus (for example by a douche) before the exam, to avoid false results. The procedure is usually just slightly painful, because of the neuroanatomy of the cervix. However, this can depend on the patient's anatomy, the skill of the practitioner, psychological factors, and other conditions. Results usually take about 3 weeks. Slight bleeding, cramps, and other discomfort can occur afterwards. Popular culture | ||||||||
|
| |||||||||
 |
|
| |